1. Field of the Invention
The present invention relates to an image forming process and apparatus therefor wherein surface potential of a recording member is sensed and image formation is controlled in response to output of the potential sensing.
2. Description of the Prior Art
In a conventional image forming apparatus for obtaining a visible image by forming an electrostatic latent image on a recording member and developing the latent image, it has been difficult to achieve stable image formation due to fluctuation of static potential on the recording member caused by an unstable output of the charger for latent image formation resulting from eventual variation in circumferential factors such as temperature and moisture. Also in consecutive latent image formations on a photosensitive member, photosensitive characteristics thereof in an image formation cycle are affected by the preceding image formation cycle. This is due to the fact that the photosensitive member has a certain memory property which is dependent on the conditions of preparation thereof, so that in consecutive image formation there inevitably appears a certain fluctuation in surface potential even if a constant exposure is given to the photosensitive member.
In an image forming apparatus utilizing an electrophotographic process comprising the steps of charging, exposure, development and image transfer, a non-imaged area not exposed to the imaging light is generated subjected to charge elimination, by exposure to a lamp generally called a blank exposure lamp, in order to prevent eventual development of the non-imaged area.
It was therefore considered to expose a non-imaged area of the photosensitive member to a determined amount of light of the blank exposure lamp and to control the charger or the developing bias according to the surface potential measured on the thus exposed area. In such a case, however, it is to be noted that the measurement of surface potential generated by the blank exposure lamp becomes meaningless in case the amount of light exceeds a certain determined level as the photosensitive member becomes saturated as shown in FIG. 8.
For this reason the amount of blank exposure for the measurement should be located within so-called dynamic range wherein the potential varies according to the amount of light. Stated differently the blank exposure lamp should provide a somewhat smaller amount of light, which will be called a weak blank exposure. The charge elimination conducted with such weak blank exposure will leave an uneven electric field due to carriers (electrons and holes) generated in the photosensitive layer. If left standing in this state, the carriers shift to metastable state, thus forming electron traps or hole traps and resulting in an uneven electric field. In the case of a 3-layered photosensitive member composed of an insulating layer, a photoconductive layer and a metal layer in succession from the surface thereof, the uneven electric field inside the photosensitive layer can be eliminated if the photosensitive member is subjected to overall or whole surface light exposure after charge elimination since the photoconductive layer is rendered conductive. However the surface charge is dissipated spontaneously or by contact with the developing brush or the cleaning blade after prolonged standing, whereby an uneven electric field is formed within the photosensitive layer to undesirably affect the succeeding latent image formation.
Also the charger output, developing bias voltage, exposure lamp power etc. have been regulated by servicemen on the basis of measurement of the surface potential on the recording member. In such measurement, the servicemen are required to memorize plural data on light and dark potentials of a latent image formed on the recording member, and such operation has been extremely tedious for them.
Furthermore, in a conventional image forming apparatus such as a copier, the function of the apparatus can only be verified by the drive of the entire apparatus, and it has not been possible to inspect the function of each component.